Question

1. What are the additional factors that might affect capacity and speed on freeways (hint: they don’t always exist, and the adjustment is not carried out if they are irrelevant in a given problem)? How do you make these adjustments?

1. What are the critical geometric parameters for a weaving section analysis?

3. What are the three macroscopic parameters in traffic flow? Which parameters was considered as the independent variable in class (as the switching point between travelers intending to make a trip, and them starting a trip)?

Answer 1

There are many factors affect the capacity and speed on freeways. Few of them are such as precipitation,lighting conditions, Traffic interruptions/restrictions,No. of lanes and Lane width etc. These factors always affect the roads surfaces.But there are some additional factors which also affect the freeways sometimes. Those are such as directional distribution and lane distribution,merge, diverge etc. I explained below why these are affects sometimes only..

Directional distribution:-

1.Distribution of direction of traffic is majorly affect the the capacity and speed on freeways.

2.Some roadways are connected with major sub roads or minor sub roads. Because of that, the some of the traffic diverts to those directions. But ,not all the freeways contain such roads.

3.So, the freeways which connect with such roads will be disturbed when the vehicles take diversion. So, the direction of such vehicles affects the remaining vehicular traffic.

4.To overcome this situations, the government provide the flyover bridges. However, this factor affect the capacity and speed on freeways.

Lane distribution:-

1.Improper lane distribution sometimes affects on the freeways.

2.In some places, the multiple lanes suddenly become half of their original width due to various reasons.

3.Then, each vehicles moves near to others gradually, and traffic becomes get congested. Then, the speed of the vehicles will reduce and sometimes it reduces to zero when the traffic becomes much congested.

4.Then, more vehicles will stay on the roads. The results will becomes worse. But,it will be normal when the width of the freeways gets wider.

5.In the rainy seasons and cold places the moisture stays on the upper surface of the freeways. It becomes wet.

6.But its common in every places. And the merges and diverges affect the capacity and speed on freeways.

7.If we provide proper lane distribution, we can adjust the bad affects.

8.If the reduction of the road widths is must, then we should reduce the width of the road gradually but not suddenly.

9.Gradual reduction of roadways somehow escape the road from bad results.

10.And we must provide the side connected sub roads where the more area is available.

11.Then the affect of direction distribution will be less. We will not get much troubles.

There are majorly some critical geometric parameters for a weaving section analysis. Those are such as weaving length, weaving width ( entry width and exit width), proportion of weaving traffic or weaving ratio.

The parameters of traffic flow are two types.

1.Microscopic parameters

2.Macroscopic parameters

Macroscopic parameters:- Three macroscopic parameters are such as Flow, speed and density.

Flow:- The number of vehicles passing a point in a given time period usually expressed as an hourly flow rate.

Speed:- The second fundamental traffic flow characteristic is speed. There are two ways to measure speed; Time-mean-speed and space-mean-speed. Time-mean-speed  is calculated from the individual speed recorded for vehicles passing a point over a selected time period. We calculate space-mean-speed by dividing the average travel time by the measured distance.

Density:- The number of vehicles occupying a unit length of roadway is called density. Traffic density is the third fundamental traffic flow characteristic. It is an important characteristic that engineers can use in assessing traffic performance from the point of view of users and system operators.The easiest way to visualize traffic density is to consider an aerial photograph of a highway section.

Density is the dependent variable and speed and flow are independent variables. Flow-density curve and speed-density curve shows the linear relationship and we get non-linear regression model. Negative sign in flow speed equation shows the negative behavior of the curve.